But didn't this thread just arrive at the conclusion that radiant damage is an inherent part of the paladin's mark?
You are confusing the marked condition for the ability that the paladin uses most often to apply the marked condition.
Here's an example of something, a parallel, so you can understand what I'm talking about here.
Let's say you have some class ability, call it Clever Attack Stance.
'While this stance is active, you may take a standard action to shift one square and then make a basic attack.'
Now, if I were a warlord, and you were in this stance, if I used Commander's Strike to give you a free melee basic attack, would you then think that you'd shift as well? Of course not. The basic attack is part of the effect of Clever Attack Stance--but you wouldn't call Clever Attack Stance a basic attack!
The same goes for Divine Challenge.
It applies the marked condition, and some other stuff as well. That other stuff happens to be a penalty for violating the mark granted by Divine Challenge, but that's not really the point.
If -I- use an ability to grant the marked condition, and make you the marker, that's not the same thing as -you- using the power Divine Challenge. Therefore, all that applies is the marked condition, and nothing else.
The reason Fighters and Wardens work differently is that the ability they have that marks is a seperate distinct thing, that ONLY marks. It doesn't -do- anything else. However, they -also- have a complimentary ability that punishes foes marked by them. It doesn't care -how- the creature was marked, because it's a seperate ability than what applied the mark in the first place.
(This is also why Divine Sanction came about, and why Swordmages have feats and powers that apply an Aegis to multiple targets, as 'the marked condition' isn't sufficient to trigger their penalties.)
